1. Field of Invention
This invention is directed to systems and methods for positioning a substrate, such as, for example, paper, in a printing device.
2. Description of Related Art
In various reproduction systems, including xerographic printing, the control and registration of the position of imageable surfaces such as photoreceptor belts, intermediate transfer belts, if any, and/or images on such imageable surfaces, and the control and registration of images transferred to and developed on a substrate, such as for example, a sheet of paper, involve both initial and process control methods.
The registration of images on either or both axes, i.e., the lateral axis and/or the process direction axis, relative to the image bearing surface and to one another, includes adjusting the position or timing of the medium sheet with respect to the image forming system.
Paper skew is the angular deviation of the longitudinal axis of the substrate in the process direction and/or the angular deviation of the lateral axis of the substrate perpendicular to the process direction. The lateral edges are the edges of the sheet which are substantially parallel to the process direction. The process edges are edges of the sheet which are substantially perpendicular to the process direction. The process edges may be referred to as the leading edge and the trailing edge.
Conventional image on sheet or image on paper setup/calibration procedures detect, and correct for, any registration errors due to paper skew, and process edge registration errors in the process direction and/or lateral edge registration errors.
Various systems and methods have been developed to control registration of a developed image on paper by controlling medium sheet placement with respect to the developed image system. Examples of such registration systems include those described in U.S. Pat. Nos. 5,094,442; 5,555,084; 5,725,211; 5,794,176; 5,848,344; 5,930,577; 6,019,365; 6,137,989; 6,168,365; 6,168,153; 6,173,952; 6,373,042 and 6,374,075, each of which is incorporated herein by reference in its entirety.
U.S. Pat. No. 5,930,577 to Forsthoefel et al. discloses xerographic systems and methods for registering a first image on a first side of a substrate and a second image printed on a second side of the substrate. A sensor detects a leading edge and a trailing edge of the substrate while an encoder operatively connected to the motor of a motor driven transport produces a number of pulses per revolution. A counter counts the number of encoded pulses between the leading edge and the trailing edge. The controller determines the width of the substrate from the number of counted encoder pulses and from the distance the substrate advances per encoder pulse. The controller controls the document transport to position the substrate at the transfer station so that the second image is registered with the first image.
U.S. Pat. No. 5,094,442 to Kamprath et al. describes lateral and longitudinal simplex sheet position registration systems and methods which use sheet leading edge sensors to detect the transverse, longitudinal and skew positioning of a sheet in the sheet feed path and change sheet drive parameters to adjust for sheet mis-positioning.
U.S. Pat. No. 6,173,952 to Richards et al. describes systems and methods for simplex and/or duplex sheet registration in which selected sheets having a variety of sheet widths transversely of the sheet process path and are partially rotated by a transversely spaced-apart pair of differentially driven sheet steering nips. A control signal proportional to the width of an image substrate sheet to be moved in the process direction is obtained, and automatically increasing or decreasing the transverse spacing between the transversely spaced-apart pair of differentially driven sheet steering nips is automatically increased or decreased in response to a control signal indicative of an increasing or decreasing width of an image substrate sheet. A sheet length control signal is provided to a controller. The sheet length control signal may be generated by a conventional sheet length sensor measuring the sheet transit time between trail edge and lead edge passage of a sheet past a sensor, which may be mounted upstream of the sheet input into the process path. Alternatively, sheet length information may already be provided in the controller. Clean new sheets, or sheets already printed on one side being returned by a duplexer for re-registration, having a variety of sheet lengths may be reliably input fed and de-skewed and/or side registered by increasing the number of nip units spaced further upstream.
U.S. Pat. No. 5,794,176 to Milillo, describes adaptive electronic sheet registration systems and methods. A translating electronic registration (TELER) sheet drive roll system provides a very accurate method of correcting mis-alignment of sheets using speed controlled drive rolls to correct for skew mis-positioning and longitudinal sheet registration. An adaptive registration device provides continuous feedback from copies made earlier about sheet during operation of the electronic roll system. The number of machine clocks that elapse between the time light exposure of an original, called “flash”, occurs until the exact instant that the trailing ends of a sheet reaches a specified point in the sheet process path is determined. A running average of the machine clocks for two sets of three registers is maintained, one set of three registers for longitudinal sheet registration and a second set of three registers for skew correction. The values for the current running average are used to adjust the algorithms which control longitudinal and skew motions of the copy sheets following the first copy sheet. The process is repeated throughout the copy operation. Because errors introduced through the TELER nip deformations area function of paper weights and sizes, and each of the paper supply drawers can have a different size of paper, a separate set of registers is dedicated to each supply drawer for storage of adaptive registration parameters. This minimizes optimizing the number of machine clocks when a copy machine operator switches paper supply drawers. The appropriate number of sheets for which registration information should be maintained can vary, and a disclosed example is averaging over three sheets.
U.S. Pat. No. 5,848,344 to Milillo et al. describes a single unit copy media registration module which also uses an adaptive electronic registration system that provides continuous feedback about errors measured during operation of an electronic drive roll system and the adjustments that are made to correct them. A running average of the difference between actual substrate measurements and set up values is maintained in system memory and appropriate changes are made to algorithms that control associated motors to continually optimize substrate registration performance.
U.S. Pat. No. 6,019,365 to Matsumura describes xerographic substrate/sheet alignment systems that correct skew and side mis-registration of a duplex sheet to achieve proper registration of images on opposite sides of a single substrate/sheet. The edge of a sheet is detected while the sheet is being conveyed. In response to the result of the sheet side edge detection, the direction in which the sheet is rotated and/or shifted is controlled to simultaneously correct the skew and side mis-registration of the sheet.
U.S. Pat. Nos. 6,168,153 and 6,173,952 to Richards et al. describe sheet handling systems in a reproduction apparatus to correct the skew and/or transverse position sheets having a wide range of lengths in the process direction. The systems use a plurality of spaced apart sheet feed nips and may apply a control signal proportional to the width of the sheet.
U.S. Pat. No. 6,374,075 to Benedict et al. describes a high accuracy sheet cross-process registration system. In the simplex mode, a smart remote uses a CCD lateral sensor to measure the sheet lateral input position and input sheet skew. After the registration, the smart remote uses the CCD lateral sensor to check how well it did in reaching the lateral and skew targets. For the duplex mode, the fine registration correction is the same as in the simplex mode except that a process edge sensor on the sheet trail edge is used, eliminating the influence of sheet length variations on registration accuracy.
U.S. Pat. No. 5,555,084 to Vetromile et al. describes simplex and duplex sheet registration systems and methods. For simplex registration, a detector senses a common physical edge of a sheet when calculating a sheet's distance from a toner image at a transfer station. Sensors measure the lead edge of a sheet between sheet corners with reference to target marks and the sheet's trail edge on its duplex (back side) pass. Alternatively, the sensors may measure the trail edge of a simplex sheet and a lead edge of a duplex sheet. For the back side (duplex) pass, the sheet is registered to the trail edge of the sheet between corners. After image, sheet cut tolerance is shifted to the trail edge between sheet corners on the back (duplex) side of the sheet. Thus, the sheet-to-image registration shifts image offsets to a common edge of the sheet.
U.S. Pat. No. 5,725,211 to Blanchard et al. describes systems and methods for reducing and/or eliminating registration error during duplex printing in a multi-pass xerographic printing system. The images to be printed are aligned with a common physical edge of a sheet by using a sheet's lead edge on a simplex pass and the sheet's trail edge on a duplex pass. Common edge registration shifts image offset to a common edge of a sheet to reduce and/or eliminate image registration due to sheet cut tolerances.
U.S. Pat. No. 6,373,042 to Kretschmann et al. describes a registration system for a digital printer designed to ensure that images on both sides of a sheet are in registration with each other. In an embodiment, two types of image placement control occur. For sheets traveling through a feed path, a running average of measurements of the location of the side edge for a set of sheets apparatus, such as a running average of the last three sheets, is maintained, and this running average is used to control the placement of images on a subsequent sheet at any particular time. Further, the precise positions of side edges of sheets passing through the duplex path is measured by an optical sensor and reported to the image placement controller. A running average of the edge positions of previously-fed sheets can be used for controlling the placement of images on subsequent sheets passing through the duplex path. Further, and possibly in addition, by comparing the running averages of the side edge positions of sheets coming through the feed path and the duplex path, a “shift factor” or mathematical relationship between the relative positions of sheets coming through the feed path and the duplex path can be obtained. It is often found that the passage of a sheet through the duplex path often results in a side-to-side shift of the sheets passing therethrough, and the shift is fairly consistent for all sheets going through the path in a particular machine. By taking this consistent shift, as symbolized by the calculated shift factor, into account while the printer is running, the image placement controller can control the marking device to ensure registration of the first side image with the second side image on a single sheet.
Other, more computationally sophisticated techniques are also disclosed in the 042 patent. For instance, if the computing power available to the printing apparatus is fast enough, a system can be provided in which for a single sheet, the precise location of the sheet is determined immediately before the sheet is fed into the marking device, and the marking device is controlled to place an image with precision relative to the determined location of the side edge of the sheet. Further, when a the same sheet is duplexed, the process can be repeated using the side edge location as determined from a sensor in the duplex path. Another variation is to use a precise measurement of the side edge location of the sheet being printed in combination with a derived shift factor as determined by the difference in average side edge locations in the feed path and the duplex path.
U.S. Pat. No. 6,137,989 to Quesnel describes a simplex sheet registration system using an integral array sensor to measure the position of a sheet based on the number of pixels of the sensor which are covered by the edge of the sheet.